Abstract:

Aims: Metamorphosis is a common character of insect development, wherein larval and adult insects exhibit significant differences in their resource requirement and utilization efficiency. Exploring the variations in niche and fitness difference in different development stages among competing insects can enhance our comprehension of insect species coexistence and community formation. Drosophila melanogaster and D. immigrans, two widely distributed Drosophila species, cohabit during the same season and both feed on decaying fruit. This study aims to explore the shift in ontogenetic niche and fitness difference between these two Drosophila flies, thereby undercovering the underlying mechanisms that facilitate their coexistence.
Methods: We set up microcosm experiments to estimate the inter- and intra-species competition coefficients, and the niche overlap and fitness difference of two Drosophila species. We then investigated the resource competition between adult flies for oviposition sites and between larval flies for food resources. Ultimately, we analyzed the probability of coexistence between the flies in their larval and adult stages using modern coexistence theory.
Results: The results showed that D. melanogaster exhibited greater fitness than D. immigrans and possessed a higher probability of winning in competition. Furthermore, adult D. immigrans demonstrated superiority in competing for oviposition sites compared to D. melanogaster, while larval D. melanogaster displayed higher nutrient efficiency than D. immigrans. However, there is significant overlap in the resources required by both species during their adult and larval stages. The competition outcomes in both larval and adult stages were predominantly determined by the sequence of resource access.
Conclusions: According to our competition experiments involving two Drosophila species, we have made an intriguing observation: two species can exhibit excellent competitive abilities during different developmental stages, seemingly enhancing the coexistence of these species. However, the presence of substantial niche overlap, leading to priority effects among the competing pairs, ultimately prevents their coexistence. Furthermore, the diverse competition strategies employed by the two Drosophila species offer an explanation for the victor in cases involving priority effects. Consequently, our findings provide valuable insights into the significance of developmental stages and phenotypic plasticity in species coexistence.

Key words: competitive exclusion, Drosophila, developmental stage, species coexistence, niche, modern species coexistence theory